Fourteen people were arrested in Germany and Denmark, including three Syrian brothers, accused of planning a bomb attack.
The Danish intelligence service, PET, said the suspects were arrested in an operation for having "planned one or more terror attacks or having participated in attempted terror acts".
It did not provide information on the plots, but some details were released in Germany.
One suspect was arrested in Germany while the rest were detained in Denmark. Seven of the Danish suspects were already in custody.
PET said the alleged plotters "gathered ingredients and components for the manufacture of explosive materials, as well as weapons or having helped".
"It is still PET's assessment that the terror threat against Denmark is serious and that this concrete matter does not change this assessment," the intelligence service said.
German prosecutors provided more details about the three brothers from Syria.
The men, aged 33, 36 and 40, were charged with planning a serious act of violence endangering the state, said prosecutors in the town of Naumburg, in Saxony-Anhalt state.
"In January of this year, they are alleged to have been involved in the purchase of several kilograms of chemicals that can be used to manufacture explosive devices," prosecutors said.
Two of the suspects were arrested in the Danish operation, where the chemicals were also seized, while the third was arrested in the German state of Hesse.
Police seized 10 kilograms of gunpowder and fuses in the town of Dessau in Saxony-Anhalt, prosecutors said.
Since 2013, the number of Islamists in Germany who are considered dangerous has increased fivefold to 615, according to security services.